Episode Details

How We Eat

Most of us think we know what we eat. However, nutrition researchers have learned a frustrating lesson over the years: asking people what they ate yesterday is often less accurate than anyone would like. Although food diaries and surveys can provide useful information, memories are imperfect, snacks are easily forgotten, and portion sizes tend to grow smaller in retrospect. Consequently, some of the most important nutrition research takes place in a setting that is both expensive and surprisingly simple—a metabolic ward, where every meal is prepared, every serving is weighed, and every leftover bite is measured.

That approach is exactly what researcher Kevin Hall and his colleagues used in a landmark study at the NIH. Participants were given two different diets, one based largely on ultra-processed foods and another built around minimally processed foods. Importantly, the volunteers could eat as much as they wanted. Nobody instructed them to count calories, restrict portions, or lose weight. Nevertheless, participants consumed about 500 more calories per day when eating the ultra-processed diet. The same people, living in the same environment, produced dramatically different results simply because the food changed.

Obesity in the US and Ultra-Processed Foods

As a result, the study raised an intriguing question. If ultra-processed foods can influence calorie intake to that degree, why isn't everyone obese? After all, ultra-processed foods make up a large portion of the modern food supply. Grocery stores are filled with them, convenience stores specialize in them, and many restaurants depend on them. Yet despite widespread exposure to the same food environment, some people seem relatively unaffected while others struggle with appetite, cravings, and weight gain.

Prego and Vanishing Calories

To understand how we arrived here, it helps to step back a few decades. During the latter half of the twentieth century, food companies increasingly turned to scientists, statisticians, and sensory researchers to understand consumer behavior. One of the most influential figures was Howard Moskowitz, a researcher who discovered that there was no single perfect food. Instead, he found that consumers tended to cluster into different preference groups. Some people preferred sweeter products, others wanted more texture, and still others favored stronger flavors. As a result, food manufacturers stopped searching for one ideal product and began creating multiple versions designed to appeal to different consumers.

Meanwhile, another researcher, Steven Witherly, focused on a different question. Rather than asking what people preferred, he explored why certain foods were so rewarding. His work highlighted the importance of texture, aroma, crunch, temperature, and mouthfeel. In other words, food is not simply taste. Instead, it is a complex sensory experience involving multiple signals that influence how satisfying a meal feels.

One of Witherly's most memorable concepts is known as vanishing caloric density. Certain foods, particularly puffed snacks, dissolve quickly in the mouth and create the sensation that they have almost disappeared. Although the calories remain, the physical experience of eating them can feel surprisingly brief. Consequently, these foods may be easier to consume in larger quantities before the body's normal satiety signals fully catch up. While that does not make such foods inherently bad, it does help explain why some snacks seem to empty themselves once the bag is opened.

Ultra-Processed Foods and GLP-1

At the same time, the modern food environment has become remarkably effective at attracting attention. Food manufacturers optimize texture, flavor, aroma, and convenience, while consumers encounter those